1. Field of the Invention
This invention relates to a light transmitting system, and more particularly to a light transmitting system using optical fibers suitable for transmitting a light beam having a high energy density such as a laser beam.
2. Description of the Prior Art
Recently, material processing techniques utilizing light energy have come into practical use. Such material processing techniques are advantageous in that the material can be processed without mechanical contact, and that it is relatively easy to obtain access to the part of the material to be processed even when the part is disposed in a narrow space of complicated shape.
The concept of light energy processing is employed for example in such medical instruments used with an endoscope as the laser scalpel and the laser coagulator.
Generally, the instrument for carrying out the light energy processing comprises a light source such as a laser and a light transmitting system for guiding a light beam emitted from the light source to the part of the material to be processed. Ordinarily, the light transmitting system comprises a fiberoptic bundle having a light entrance face and a light exit face. The light beam emitted from the light source is caused to impinge on the entire area of the light entrance face of the fiberoptic bundle and is transmitted through each optical fiber of the bundle to emanate from the exit face thereof to strike the material to be processed. The light beam employed in light energy processing is generally a laser beam having a high energy density such as a CO.sub.2 laser, a YAG laser or an Ar laser.
The conventional light transmitting system in which the laser beam emitted from the laser is caused to impinge on the entire area of the entrance face of the fiberoptic bundle gives rise to some problems when the light output power of the laser is increased. When the light output power of the laser is increased beyond a certain level the transmission efficiency of the light transmitting system is substantially lowered; that is, a substantial amount of the light energy is lost in the space between the optical fibers of the bundle, this space being occupied by adhesive for binding the optical fibers together to form the bundle and not contributing to the transmission of the light energy. Further, the adhesive between the optical fibers is deteriorated by the light energy and the deteriorated adhesive damages and contaminates the entrance face of the bundle. Especially, when the optical fibers used are of the core/cladding type, the energy loss at the light entrance face may be as high as 70 to 80% since the cladding does not contribute to light energy transmission.
These problems can be overcome by transmitting the light energy through a single optical fiber having a relatively large outer diameter of, for example, 300-400.mu.. However, the optical fiber of such a large diameter has poor flexibility, whereas it is desirable for the light transmitting system to have high flexibility at least at the portion near the light exit face so that the light beam emanating therefrom can be easily directed in the required direction. Especially when the light energy processing instrument is used with an endoscope, the light transmitting system should be flexible enough to be bendable along with the endoscope. For example, an endoscope for the stomach or the duodenum may sometimes be bent to form an arc having a radius of curvature of about 15 mm.
In order to obtain such a high flexibility with a single fiber, the diameter of the fiber must be as small as 150.mu. (about 100.mu. at its core). However, a thin optical fiber even a heat resistant fiber having a quartz core, would be damaged by heat if a laser beam of high energy density should be transmitted therethrough.
Thus there has been a great demand for a light transmitting system which has high flexibility and can transmit light having high energy density without substantial loss of the light energy.
In the medical use of light energy processing, the affected part is exposed to a light spot. It is preferred that the energy level be uniform over the entire area of the light spot so that a uniform effect can be obtained within the spot. If the light energy is not uniformly distributed throughout the light spot, the area of the affected part subjected to the lower energy will not be properly treated. Accordingly, the light spot must be moved so that the entire area of the affected part is exposed to the light of the higher energy level. However, provision of a mechanism for moving the light spot would adversely affect the flexbility of the entire endoscope assembly. If the output power of the laser is increased to raise the energy level of the lower energy area up to a level high enough for the treatment, then the area of the affected part subjected to the higher energy level might possibly be damaged.